Issued last summer, the rules are the centerpiece of the White House’s climate-change-fighting agenda, and they play a big part in the recent, tepid optimism about global warming. Without the proposal of the plan, the United States couldn’t have secured the Paris Agreement, the first international treaty to mitigate greenhouse-gas emissions, last December. And without the adoption of the plan, the United States almost certainly won’t be able to comply with that document. If the world were to lose the Paris Agreement—which was not a total solution to the climate crisis, but meant to be a first, provisional step—years could be lost in the diplomatic fight to reduce climate-change’s dangers.

The plan’s ultimate legal future is unclear, for reasons I’ll get into in a minute, but the ruling is possibly devastating for the climate on a short-term basis. Moreover, it represents an early weakness in the new global strategy to mitigate climate change.

Here’s why: It had long been clear that many states would challenge the EPA regulations. Within hours of the rules’ final publication last fall, two dozen states sued the government to stop their implementation; eventually, 29 states in total joined the lawsuit. But some climate advocates hinted that these legal protests wouldn’t matter. Simply by existing, they said, the rules communicated that America was moving its energy system away from fossil fuels. Global investors would have to follow suit, they said, and divest from fossil fuels. In other words, even if the Supreme Court eventually struck the Clean Power Plan down, the damage would be done.

The idea wasn’t for naught. Coal stocks tanked over the last year, and many of the largest American coal companies have filed for bankruptcy. In fact, opponents of the plan cited this exact effect in their brief: The “EPA hopes that, by the time the judiciary adjudicates the legality of the Power Plan, the judicial action will come too late to make much if any practical difference,” said one brief from the Harvard law professor Laurence Tribe. He called the plan a “targeted attack on the coal industry.”

The court’s stay means that that effect might go on pause, at least domestically. It could also push the entire timeline for the regulations forward. Previously, states had to submit compliance plans by this summer, though they could request an extension to 2018. But now, the D.C. circuit isn’t scheduled to hear the EPA’s case until June, and any appeal wouldn’t wind up in front of the Supreme Court until the fall at the earliest. By that time, of course, the White House will have changed hands—which means, short of defending this regulation, the Obama administration is running out of ways to push climate in the direction it wants.

How much danger is the Clean Power Plan ultimately in? The Court’s stay is so “unprecedented”—even The New York Times calls it that, in stolid reporter voice—that no one knows for sure.

On the one hand, the high court has never before blocked federal regulation while a case about it was being heard by an appeals court. On the other, the Supreme Court is the reason why the Clean Power Plan could exist in the first place. The EPA issued the rules under the Clean Air Act, a 1970 statute that forms much of the basis of federal environmental law and which requires the government to limit “air pollutants” that might harm public welfare. In 2007, the Supreme Court ruled that “greenhouse gases fit well within the Act’s capacious definition of ‘air pollutant’” and thus the EPA was obligated to regulate them. The Bush administration’s EPA never quite got around to it. But the Obama administration eventually did, and quite ambitiously. Since 2010, as well, this president’s EPA has won most of its fights about the act.

Somewhat oddly, if the Clean Power Plan gets sullied by the Court, a future (Democratic) president’s EPA could take a more direct approach. Legal challenges to the rules have tended to focus on their mechanism under the Clean Air Act, not their ultimate target. If this plan gets thrown out, the act would allow the agency to more directly command and control carbon-dioxide emissions. The agency took a broader, gentler approach with its current plan; if it’s compelled to stick closer to the letter of the law, it could order far deeper cuts.

In a way, the Clean Power Plan mirrors the world’s approach. The world’s post-Paris climate strategy has been to talk a better game than it was actually playing. By adopting an ambitious climate agreement, and implementing incremental carbon-mitigating rules in many countries, the international community hoped to tell investors that it was time to get out of the fossil-fuel business. As John Kerry put it, by “sending a message to the global marketplace,” the world would transition away from coal, oil, and gas far more easily than a directly regulated (and politically impossible) change. But in the United States—the home of the only major political party that rejects climate science—some of the sellers in that marketplace are talking back.

The Clean Power Plan—and the EPA’s resolve to regulate greenhouse gases—depends on the same ultimate mechanism it always did: that Democrats win the White House in November. If they win, they can defend the regulation, alter it as needed, and they have time to favorably adjust the Court’s balance on future cases. And if the Republicans win? Who knows what happens, but it’s worth noting that no remaining GOP candidate supports regulation to halt climate change’s advance. Donald Trump and Ted Cruz don’t even think it’s real.

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Robinson Meyer is a staff writer at The Atlantic, where he covers climate change and technology.